xref: /freebsd-10.0-release/lib/libc/regex/regcomp.c

/*-
 * Copyright (c) 1992, 1993, 1994 Henry Spencer.
 * Copyright (c) 1992, 1993, 1994
 *	The Regents of the University of California.  All rights reserved.
 *
 * This code is derived from software contributed to Berkeley by
 * Henry Spencer.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 4. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 *
 *	@(#)regcomp.c	8.5 (Berkeley) 3/20/94
 */

#if defined(LIBC_SCCS) && !defined(lint)
static char sccsid[] = "@(#)regcomp.c	8.5 (Berkeley) 3/20/94";
#endif /* LIBC_SCCS and not lint */
#include <sys/cdefs.h>
__FBSDID("$FreeBSD: head/lib/libc/regex/regcomp.c 170528 2007-06-11 03:05:54Z delphij $");

#include <sys/types.h>
#include <stdio.h>
#include <string.h>
#include <ctype.h>
#include <limits.h>
#include <stdlib.h>
#include <regex.h>
#include <runetype.h>
#include <wchar.h>
#include <wctype.h>

#include "collate.h"

#include "utils.h"
#include "regex2.h"

#include "cname.h"

/*
 * parse structure, passed up and down to avoid global variables and
 * other clumsinesses
 */
struct parse {
	char *next;		/* next character in RE */
	char *end;		/* end of string (-> NUL normally) */
	int error;		/* has an error been seen? */
	sop *strip;		/* malloced strip */
	sopno ssize;		/* malloced strip size (allocated) */
	sopno slen;		/* malloced strip length (used) */
	int ncsalloc;		/* number of csets allocated */
	struct re_guts *g;
#	define	NPAREN	10	/* we need to remember () 1-9 for back refs */
	sopno pbegin[NPAREN];	/* -> ( ([0] unused) */
	sopno pend[NPAREN];	/* -> ) ([0] unused) */
};

/* ========= begin header generated by ./mkh ========= */
#ifdef __cplusplus
extern "C" {
#endif

/* === regcomp.c === */
static void p_ere(struct parse *p, wint_t stop);
static void p_ere_exp(struct parse *p);
static void p_str(struct parse *p);
static void p_bre(struct parse *p, wint_t end1, wint_t end2);
static int p_simp_re(struct parse *p, int starordinary);
static int p_count(struct parse *p);
static void p_bracket(struct parse *p);
static void p_b_term(struct parse *p, cset *cs);
static void p_b_cclass(struct parse *p, cset *cs);
static void p_b_eclass(struct parse *p, cset *cs);
static wint_t p_b_symbol(struct parse *p);
static wint_t p_b_coll_elem(struct parse *p, wint_t endc);
static wint_t othercase(wint_t ch);
static void bothcases(struct parse *p, wint_t ch);
static void ordinary(struct parse *p, wint_t ch);
static void nonnewline(struct parse *p);
static void repeat(struct parse *p, sopno start, int from, int to);
static int seterr(struct parse *p, int e);
static cset *allocset(struct parse *p);
static void freeset(struct parse *p, cset *cs);
static void CHadd(struct parse *p, cset *cs, wint_t ch);
static void CHaddrange(struct parse *p, cset *cs, wint_t min, wint_t max);
static void CHaddtype(struct parse *p, cset *cs, wctype_t wct);
static wint_t singleton(cset *cs);
static sopno dupl(struct parse *p, sopno start, sopno finish);
static void doemit(struct parse *p, sop op, size_t opnd);
static void doinsert(struct parse *p, sop op, size_t opnd, sopno pos);
static void dofwd(struct parse *p, sopno pos, sop value);
static void enlarge(struct parse *p, sopno size);
static void stripsnug(struct parse *p, struct re_guts *g);
static void findmust(struct parse *p, struct re_guts *g);
static int altoffset(sop *scan, int offset);
static void computejumps(struct parse *p, struct re_guts *g);
static void computematchjumps(struct parse *p, struct re_guts *g);
static sopno pluscount(struct parse *p, struct re_guts *g);
static wint_t wgetnext(struct parse *p);

#ifdef __cplusplus
}
#endif
/* ========= end header generated by ./mkh ========= */

static char nuls[10];		/* place to point scanner in event of error */

/*
 * macros for use with parse structure
 * BEWARE:  these know that the parse structure is named `p' !!!
 */
#define	PEEK()	(*p->next)
#define	PEEK2()	(*(p->next+1))
#define	MORE()	(p->next < p->end)
#define	MORE2()	(p->next+1 < p->end)
#define	SEE(c)	(MORE() && PEEK() == (c))
#define	SEETWO(a, b)	(MORE() && MORE2() && PEEK() == (a) && PEEK2() == (b))
#define	EAT(c)	((SEE(c)) ? (NEXT(), 1) : 0)
#define	EATTWO(a, b)	((SEETWO(a, b)) ? (NEXT2(), 1) : 0)
#define	NEXT()	(p->next++)
#define	NEXT2()	(p->next += 2)
#define	NEXTn(n)	(p->next += (n))
#define	GETNEXT()	(*p->next++)
#define	WGETNEXT()	wgetnext(p)
#define	SETERROR(e)	seterr(p, (e))
#define	REQUIRE(co, e)	((co) || SETERROR(e))
#define	MUSTSEE(c, e)	(REQUIRE(MORE() && PEEK() == (c), e))
#define	MUSTEAT(c, e)	(REQUIRE(MORE() && GETNEXT() == (c), e))
#define	MUSTNOTSEE(c, e)	(REQUIRE(!MORE() || PEEK() != (c), e))
#define	EMIT(op, sopnd)	doemit(p, (sop)(op), (size_t)(sopnd))
#define	INSERT(op, pos)	doinsert(p, (sop)(op), HERE()-(pos)+1, pos)
#define	AHEAD(pos)		dofwd(p, pos, HERE()-(pos))
#define	ASTERN(sop, pos)	EMIT(sop, HERE()-pos)
#define	HERE()		(p->slen)
#define	THERE()		(p->slen - 1)
#define	THERETHERE()	(p->slen - 2)
#define	DROP(n)	(p->slen -= (n))

#ifndef NDEBUG
static int never = 0;		/* for use in asserts; shuts lint up */
#else
#define	never	0		/* some <assert.h>s have bugs too */
#endif

/* Macro used by computejump()/computematchjump() */
#define MIN(a,b)	((a)<(b)?(a):(b))

/*
 - regcomp - interface for parser and compilation
 = extern int regcomp(regex_t *, const char *, int);
 = #define	REG_BASIC	0000
 = #define	REG_EXTENDED	0001
 = #define	REG_ICASE	0002
 = #define	REG_NOSUB	0004
 = #define	REG_NEWLINE	0010
 = #define	REG_NOSPEC	0020
 = #define	REG_PEND	0040
 = #define	REG_DUMP	0200
 */
int				/* 0 success, otherwise REG_something */
regcomp(regex_t * __restrict preg,
	const char * __restrict pattern,
	int cflags)
{
	struct parse pa;
	struct re_guts *g;
	struct parse *p = &pa;
	int i;
	size_t len;
#ifdef REDEBUG
#	define	GOODFLAGS(f)	(f)
#else
#	define	GOODFLAGS(f)	((f)&~REG_DUMP)
#endif

	cflags = GOODFLAGS(cflags);
	if ((cflags&REG_EXTENDED) && (cflags&REG_NOSPEC))
		return(REG_INVARG);

	if (cflags&REG_PEND) {
		if (preg->re_endp < pattern)
			return(REG_INVARG);
		len = preg->re_endp - pattern;
	} else
		len = strlen((char *)pattern);

	/* do the mallocs early so failure handling is easy */
	g = (struct re_guts *)malloc(sizeof(struct re_guts));
	if (g == NULL)
		return(REG_ESPACE);
	p->ssize = len/(size_t)2*(size_t)3 + (size_t)1;	/* ugh */
	p->strip = (sop *)malloc(p->ssize * sizeof(sop));
	p->slen = 0;
	if (p->strip == NULL) {
		free((char *)g);
		return(REG_ESPACE);
	}

	/* set things up */
	p->g = g;
	p->next = (char *)pattern;	/* convenience; we do not modify it */
	p->end = p->next + len;
	p->error = 0;
	p->ncsalloc = 0;
	for (i = 0; i < NPAREN; i++) {
		p->pbegin[i] = 0;
		p->pend[i] = 0;
	}
	g->sets = NULL;
	g->ncsets = 0;
	g->cflags = cflags;
	g->iflags = 0;
	g->nbol = 0;
	g->neol = 0;
	g->must = NULL;
	g->moffset = -1;
	g->charjump = NULL;
	g->matchjump = NULL;
	g->mlen = 0;
	g->nsub = 0;
	g->backrefs = 0;

	/* do it */
	EMIT(OEND, 0);
	g->firststate = THERE();
	if (cflags&REG_EXTENDED)
		p_ere(p, OUT);
	else if (cflags&REG_NOSPEC)
		p_str(p);
	else
		p_bre(p, OUT, OUT);
	EMIT(OEND, 0);
	g->laststate = THERE();

	/* tidy up loose ends and fill things in */
	stripsnug(p, g);
	findmust(p, g);
	/* only use Boyer-Moore algorithm if the pattern is bigger
	 * than three characters
	 */
	if(g->mlen > 3) {
		computejumps(p, g);
		computematchjumps(p, g);
		if(g->matchjump == NULL && g->charjump != NULL) {
			free(g->charjump);
			g->charjump = NULL;
		}
	}
	g->nplus = pluscount(p, g);
	g->magic = MAGIC2;
	preg->re_nsub = g->nsub;
	preg->re_g = g;
	preg->re_magic = MAGIC1;
#ifndef REDEBUG
	/* not debugging, so can't rely on the assert() in regexec() */
	if (g->iflags&BAD)
		SETERROR(REG_ASSERT);
#endif

	/* win or lose, we're done */
	if (p->error != 0)	/* lose */
		regfree(preg);
	return(p->error);
}

/*
 - p_ere - ERE parser top level, concatenation and alternation
 == static void p_ere(struct parse *p, int stop);
 */
static void
p_ere(struct parse *p,
	int stop)		/* character this ERE should end at */
{
	char c;
	sopno prevback;
	sopno prevfwd;
	sopno conc;
	int first = 1;		/* is this the first alternative? */

	for (;;) {
		/* do a bunch of concatenated expressions */
		conc = HERE();
		while (MORE() && (c = PEEK()) != '|' && c != stop)
			p_ere_exp(p);
		(void)REQUIRE(HERE() != conc, REG_EMPTY);	/* require nonempty */

		if (!EAT('|'))
			break;		/* NOTE BREAK OUT */

		if (first) {
			INSERT(OCH_, conc);	/* offset is wrong */
			prevfwd = conc;
			prevback = conc;
			first = 0;
		}
		ASTERN(OOR1, prevback);
		prevback = THERE();
		AHEAD(prevfwd);			/* fix previous offset */
		prevfwd = HERE();
		EMIT(OOR2, 0);			/* offset is very wrong */
	}

	if (!first) {		/* tail-end fixups */
		AHEAD(prevfwd);
		ASTERN(O_CH, prevback);
	}

	assert(!MORE() || SEE(stop));
}

/*
 - p_ere_exp - parse one subERE, an atom possibly followed by a repetition op
 == static void p_ere_exp(struct parse *p);
 */
static void
p_ere_exp(struct parse *p)
{
	char c;
	wint_t wc;
	sopno pos;
	int count;
	int count2;
	sopno subno;
	int wascaret = 0;

	assert(MORE());		/* caller should have ensured this */
	c = GETNEXT();

	pos = HERE();
	switch (c) {
	case '(':
		(void)REQUIRE(MORE(), REG_EPAREN);
		p->g->nsub++;
		subno = p->g->nsub;
		if (subno < NPAREN)
			p->pbegin[subno] = HERE();
		EMIT(OLPAREN, subno);
		if (!SEE(')'))
			p_ere(p, ')');
		if (subno < NPAREN) {
			p->pend[subno] = HERE();
			assert(p->pend[subno] != 0);
		}
		EMIT(ORPAREN, subno);
		(void)MUSTEAT(')', REG_EPAREN);
		break;
#ifndef POSIX_MISTAKE
	case ')':		/* happens only if no current unmatched ( */
		/*
		 * You may ask, why the ifndef?  Because I didn't notice
		 * this until slightly too late for 1003.2, and none of the
		 * other 1003.2 regular-expression reviewers noticed it at
		 * all.  So an unmatched ) is legal POSIX, at least until
		 * we can get it fixed.
		 */
		SETERROR(REG_EPAREN);
		break;
#endif
	case '^':
		EMIT(OBOL, 0);
		p->g->iflags |= USEBOL;
		p->g->nbol++;
		wascaret = 1;
		break;
	case '$':
		EMIT(OEOL, 0);
		p->g->iflags |= USEEOL;
		p->g->neol++;
		break;
	case '|':
		SETERROR(REG_EMPTY);
		break;
	case '*':
	case '+':
	case '?':
		SETERROR(REG_BADRPT);
		break;
	case '.':
		if (p->g->cflags&REG_NEWLINE)
			nonnewline(p);
		else
			EMIT(OANY, 0);
		break;
	case '[':
		p_bracket(p);
		break;
	case '\\':
		(void)REQUIRE(MORE(), REG_EESCAPE);
		wc = WGETNEXT();
		ordinary(p, wc);
		break;
	case '{':		/* okay as ordinary except if digit follows */
		(void)REQUIRE(!MORE() || !isdigit((uch)PEEK()), REG_BADRPT);
		/* FALLTHROUGH */
	default:
		p->next--;
		wc = WGETNEXT();
		ordinary(p, wc);
		break;
	}

	if (!MORE())
		return;
	c = PEEK();
	/* we call { a repetition if followed by a digit */
	if (!( c == '*' || c == '+' || c == '?' ||
				(c == '{' && MORE2() && isdigit((uch)PEEK2())) ))
		return;		/* no repetition, we're done */
	NEXT();

	(void)REQUIRE(!wascaret, REG_BADRPT);
	switch (c) {
	case '*':	/* implemented as +? */
		/* this case does not require the (y|) trick, noKLUDGE */
		INSERT(OPLUS_, pos);
		ASTERN(O_PLUS, pos);
		INSERT(OQUEST_, pos);
		ASTERN(O_QUEST, pos);
		break;
	case '+':
		INSERT(OPLUS_, pos);
		ASTERN(O_PLUS, pos);
		break;
	case '?':
		/* KLUDGE: emit y? as (y|) until subtle bug gets fixed */
		INSERT(OCH_, pos);		/* offset slightly wrong */
		ASTERN(OOR1, pos);		/* this one's right */
		AHEAD(pos);			/* fix the OCH_ */
		EMIT(OOR2, 0);			/* offset very wrong... */
		AHEAD(THERE());			/* ...so fix it */
		ASTERN(O_CH, THERETHERE());
		break;
	case '{':
		count = p_count(p);
		if (EAT(',')) {
			if (isdigit((uch)PEEK())) {
				count2 = p_count(p);
				(void)REQUIRE(count <= count2, REG_BADBR);
			} else		/* single number with comma */
				count2 = INFINITY;
		} else		/* just a single number */
			count2 = count;
		repeat(p, pos, count, count2);
		if (!EAT('}')) {	/* error heuristics */
			while (MORE() && PEEK() != '}')
				NEXT();
			(void)REQUIRE(MORE(), REG_EBRACE);
			SETERROR(REG_BADBR);
		}
		break;
	}

	if (!MORE())
		return;
	c = PEEK();
	if (!( c == '*' || c == '+' || c == '?' ||
				(c == '{' && MORE2() && isdigit((uch)PEEK2())) ) )
		return;
	SETERROR(REG_BADRPT);
}

/*
 - p_str - string (no metacharacters) "parser"
 == static void p_str(struct parse *p);
 */
static void
p_str(struct parse *p)
{
	(void)REQUIRE(MORE(), REG_EMPTY);
	while (MORE())
		ordinary(p, WGETNEXT());
}

/*
 - p_bre - BRE parser top level, anchoring and concatenation
 == static void p_bre(struct parse *p, int end1, \
 ==	int end2);
 * Giving end1 as OUT essentially eliminates the end1/end2 check.
 *
 * This implementation is a bit of a kludge, in that a trailing $ is first
 * taken as an ordinary character and then revised to be an anchor.
 * The amount of lookahead needed to avoid this kludge is excessive.
 */
static void
p_bre(struct parse *p,
	int end1,		/* first terminating character */
	int end2)		/* second terminating character */
{
	sopno start = HERE();
	int first = 1;			/* first subexpression? */
	int wasdollar = 0;

	if (EAT('^')) {
		EMIT(OBOL, 0);
		p->g->iflags |= USEBOL;
		p->g->nbol++;
	}
	while (MORE() && !SEETWO(end1, end2)) {
		wasdollar = p_simp_re(p, first);
		first = 0;
	}
	if (wasdollar) {	/* oops, that was a trailing anchor */
		DROP(1);
		EMIT(OEOL, 0);
		p->g->iflags |= USEEOL;
		p->g->neol++;
	}

	(void)REQUIRE(HERE() != start, REG_EMPTY);	/* require nonempty */
}

/*
 - p_simp_re - parse a simple RE, an atom possibly followed by a repetition
 == static int p_simp_re(struct parse *p, int starordinary);
 */
static int			/* was the simple RE an unbackslashed $? */
p_simp_re(struct parse *p,
	int starordinary)	/* is a leading * an ordinary character? */
{
	int c;
	int count;
	int count2;
	sopno pos;
	int i;
	wint_t wc;
	sopno subno;
#	define	BACKSL	(1<<CHAR_BIT)

	pos = HERE();		/* repetion op, if any, covers from here */

	assert(MORE());		/* caller should have ensured this */
	c = GETNEXT();
	if (c == '\\') {
		(void)REQUIRE(MORE(), REG_EESCAPE);
		c = BACKSL | GETNEXT();
	}
	switch (c) {
	case '.':
		if (p->g->cflags&REG_NEWLINE)
			nonnewline(p);
		else
			EMIT(OANY, 0);
		break;
	case '[':
		p_bracket(p);
		break;
	case BACKSL|'{':
		SETERROR(REG_BADRPT);
		break;
	case BACKSL|'(':
		p->g->nsub++;
		subno = p->g->nsub;
		if (subno < NPAREN)
			p->pbegin[subno] = HERE();
		EMIT(OLPAREN, subno);
		/* the MORE here is an error heuristic */
		if (MORE() && !SEETWO('\\', ')'))
			p_bre(p, '\\', ')');
		if (subno < NPAREN) {
			p->pend[subno] = HERE();
			assert(p->pend[subno] != 0);
		}
		EMIT(ORPAREN, subno);
		(void)REQUIRE(EATTWO('\\', ')'), REG_EPAREN);
		break;
	case BACKSL|')':	/* should not get here -- must be user */
	case BACKSL|'}':
		SETERROR(REG_EPAREN);
		break;
	case BACKSL|'1':
	case BACKSL|'2':
	case BACKSL|'3':
	case BACKSL|'4':
	case BACKSL|'5':
	case BACKSL|'6':
	case BACKSL|'7':
	case BACKSL|'8':
	case BACKSL|'9':
		i = (c&~BACKSL) - '0';
		assert(i < NPAREN);
		if (p->pend[i] != 0) {
			assert(i <= p->g->nsub);
			EMIT(OBACK_, i);
			assert(p->pbegin[i] != 0);
			assert(OP(p->strip[p->pbegin[i]]) == OLPAREN);
			assert(OP(p->strip[p->pend[i]]) == ORPAREN);
			(void) dupl(p, p->pbegin[i]+1, p->pend[i]);
			EMIT(O_BACK, i);
		} else
			SETERROR(REG_ESUBREG);
		p->g->backrefs = 1;
		break;
	case '*':
		(void)REQUIRE(starordinary, REG_BADRPT);
		/* FALLTHROUGH */
	default:
		p->next--;
		wc = WGETNEXT();
		ordinary(p, wc);
		break;
	}

	if (EAT('*')) {		/* implemented as +? */
		/* this case does not require the (y|) trick, noKLUDGE */
		INSERT(OPLUS_, pos);
		ASTERN(O_PLUS, pos);
		INSERT(OQUEST_, pos);
		ASTERN(O_QUEST, pos);
	} else if (EATTWO('\\', '{')) {
		count = p_count(p);
		if (EAT(',')) {
			if (MORE() && isdigit((uch)PEEK())) {
				count2 = p_count(p);
				(void)REQUIRE(count <= count2, REG_BADBR);
			} else		/* single number with comma */
				count2 = INFINITY;
		} else		/* just a single number */
			count2 = count;
		repeat(p, pos, count, count2);
		if (!EATTWO('\\', '}')) {	/* error heuristics */
			while (MORE() && !SEETWO('\\', '}'))
				NEXT();
			(void)REQUIRE(MORE(), REG_EBRACE);
			SETERROR(REG_BADBR);
		}
	} else if (c == '$')     /* $ (but not \$) ends it */
		return(1);

	return(0);
}

/*
 - p_count - parse a repetition count
 == static int p_count(struct parse *p);
 */
static int			/* the value */
p_count(struct parse *p)
{
	int count = 0;
	int ndigits = 0;

	while (MORE() && isdigit((uch)PEEK()) && count <= DUPMAX) {
		count = count*10 + (GETNEXT() - '0');
		ndigits++;
	}

	(void)REQUIRE(ndigits > 0 && count <= DUPMAX, REG_BADBR);
	return(count);
}

/*
 - p_bracket - parse a bracketed character list
 == static void p_bracket(struct parse *p);
 */
static void
p_bracket(struct parse *p)
{
	cset *cs;
	wint_t ch;

	/* Dept of Truly Sickening Special-Case Kludges */
	if (p->next + 5 < p->end && strncmp(p->next, "[:<:]]", 6) == 0) {
		EMIT(OBOW, 0);
		NEXTn(6);
		return;
	}
	if (p->next + 5 < p->end && strncmp(p->next, "[:>:]]", 6) == 0) {
		EMIT(OEOW, 0);
		NEXTn(6);
		return;
	}

	if ((cs = allocset(p)) == NULL)
		return;

	if (p->g->cflags&REG_ICASE)
		cs->icase = 1;
	if (EAT('^'))
		cs->invert = 1;
	if (EAT(']'))
		CHadd(p, cs, ']');
	else if (EAT('-'))
		CHadd(p, cs, '-');
	while (MORE() && PEEK() != ']' && !SEETWO('-', ']'))
		p_b_term(p, cs);
	if (EAT('-'))
		CHadd(p, cs, '-');
	(void)MUSTEAT(']', REG_EBRACK);

	if (p->error != 0)	/* don't mess things up further */
		return;

	if (cs->invert && p->g->cflags&REG_NEWLINE)
		cs->bmp['\n' >> 3] |= 1 << ('\n' & 7);

	if ((ch = singleton(cs)) != OUT) {	/* optimize singleton sets */
		ordinary(p, ch);
		freeset(p, cs);
	} else
		EMIT(OANYOF, (int)(cs - p->g->sets));
}

/*
 - p_b_term - parse one term of a bracketed character list
 == static void p_b_term(struct parse *p, cset *cs);
 */
static void
p_b_term(struct parse *p, cset *cs)
{
	char c;
	wint_t start, finish;
	wint_t i;

	/* classify what we've got */
	switch ((MORE()) ? PEEK() : '\0') {
	case '[':
		c = (MORE2()) ? PEEK2() : '\0';
		break;
	case '-':
		SETERROR(REG_ERANGE);
		return;			/* NOTE RETURN */
		break;
	default:
		c = '\0';
		break;
	}

	switch (c) {
	case ':':		/* character class */
		NEXT2();
		(void)REQUIRE(MORE(), REG_EBRACK);
		c = PEEK();
		(void)REQUIRE(c != '-' && c != ']', REG_ECTYPE);
		p_b_cclass(p, cs);
		(void)REQUIRE(MORE(), REG_EBRACK);
		(void)REQUIRE(EATTWO(':', ']'), REG_ECTYPE);
		break;
	case '=':		/* equivalence class */
		NEXT2();
		(void)REQUIRE(MORE(), REG_EBRACK);
		c = PEEK();
		(void)REQUIRE(c != '-' && c != ']', REG_ECOLLATE);
		p_b_eclass(p, cs);
		(void)REQUIRE(MORE(), REG_EBRACK);
		(void)REQUIRE(EATTWO('=', ']'), REG_ECOLLATE);
		break;
	default:		/* symbol, ordinary character, or range */
		start = p_b_symbol(p);
		if (SEE('-') && MORE2() && PEEK2() != ']') {
			/* range */
			NEXT();
			if (EAT('-'))
				finish = '-';
			else
				finish = p_b_symbol(p);
		} else
			finish = start;
		if (start == finish)
			CHadd(p, cs, start);
		else {
			if (__collate_load_error) {
				(void)REQUIRE((uch)start <= (uch)finish, REG_ERANGE);
				CHaddrange(p, cs, start, finish);
			} else {
				(void)REQUIRE(__collate_range_cmp(start, finish) <= 0, REG_ERANGE);
				for (i = 0; i <= UCHAR_MAX; i++) {
					if (   __collate_range_cmp(start, i) <= 0
					    && __collate_range_cmp(i, finish) <= 0
					   )
						CHadd(p, cs, i);
				}
			}
		}
		break;
	}
}

/*
 - p_b_cclass - parse a character-class name and deal with it
 == static void p_b_cclass(struct parse *p, cset *cs);
 */
static void
p_b_cclass(struct parse *p, cset *cs)
{
	char *sp = p->next;
	size_t len;
	wctype_t wct;
	char clname[16];

	while (MORE() && isalpha((uch)PEEK()))
		NEXT();
	len = p->next - sp;
	if (len >= sizeof(clname) - 1) {
		SETERROR(REG_ECTYPE);
		return;
	}
	memcpy(clname, sp, len);
	clname[len] = '\0';
	if ((wct = wctype(clname)) == 0) {
		SETERROR(REG_ECTYPE);
		return;
	}
	CHaddtype(p, cs, wct);
}

/*
 - p_b_eclass - parse an equivalence-class name and deal with it
 == static void p_b_eclass(struct parse *p, cset *cs);
 *
 * This implementation is incomplete. xxx
 */
static void
p_b_eclass(struct parse *p, cset *cs)
{
	wint_t c;

	c = p_b_coll_elem(p, '=');
	CHadd(p, cs, c);
}

/*
 - p_b_symbol - parse a character or [..]ed multicharacter collating symbol
 == static char p_b_symbol(struct parse *p);
 */
static wint_t			/* value of symbol */
p_b_symbol(struct parse *p)
{
	wint_t value;

	(void)REQUIRE(MORE(), REG_EBRACK);
	if (!EATTWO('[', '.'))
		return(WGETNEXT());

	/* collating symbol */
	value = p_b_coll_elem(p, '.');
	(void)REQUIRE(EATTWO('.', ']'), REG_ECOLLATE);
	return(value);
}

/*
 - p_b_coll_elem - parse a collating-element name and look it up
 == static char p_b_coll_elem(struct parse *p, int endc);
 */
static wint_t			/* value of collating element */
p_b_coll_elem(struct parse *p,
	wint_t endc)		/* name ended by endc,']' */
{
	char *sp = p->next;
	struct cname *cp;
	int len;
	mbstate_t mbs;
	wchar_t wc;
	size_t clen;

	while (MORE() && !SEETWO(endc, ']'))
		NEXT();
	if (!MORE()) {
		SETERROR(REG_EBRACK);
		return(0);
	}
	len = p->next - sp;
	for (cp = cnames; cp->name != NULL; cp++)
		if (strncmp(cp->name, sp, len) == 0 && cp->name[len] == '\0')
			return(cp->code);	/* known name */
	memset(&mbs, 0, sizeof(mbs));
	if ((clen = mbrtowc(&wc, sp, len, &mbs)) == len)
		return (wc);			/* single character */
	else if (clen == (size_t)-1 || clen == (size_t)-2)
		SETERROR(REG_ILLSEQ);
	else
		SETERROR(REG_ECOLLATE);		/* neither */
	return(0);
}

/*
 - othercase - return the case counterpart of an alphabetic
 == static char othercase(int ch);
 */
static wint_t			/* if no counterpart, return ch */
othercase(wint_t ch)
{
	assert(iswalpha(ch));
	if (iswupper(ch))
		return(towlower(ch));
	else if (iswlower(ch))
		return(towupper(ch));
	else			/* peculiar, but could happen */
		return(ch);
}

/*
 - bothcases - emit a dualcase version of a two-case character
 == static void bothcases(struct parse *p, int ch);
 *
 * Boy, is this implementation ever a kludge...
 */
static void
bothcases(struct parse *p, wint_t ch)
{
	char *oldnext = p->next;
	char *oldend = p->end;
	char bracket[3 + MB_LEN_MAX];
	size_t n;
	mbstate_t mbs;

	assert(othercase(ch) != ch);	/* p_bracket() would recurse */
	p->next = bracket;
	memset(&mbs, 0, sizeof(mbs));
	n = wcrtomb(bracket, ch, &mbs);
	assert(n != (size_t)-1);
	bracket[n] = ']';
	bracket[n + 1] = '\0';
	p->end = bracket+n+1;
	p_bracket(p);
	assert(p->next == p->end);
	p->next = oldnext;
	p->end = oldend;
}

/*
 - ordinary - emit an ordinary character
 == static void ordinary(struct parse *p, int ch);
 */
static void
ordinary(struct parse *p, wint_t ch)
{
	cset *cs;

	if ((p->g->cflags&REG_ICASE) && iswalpha(ch) && othercase(ch) != ch)
		bothcases(p, ch);
	else if ((ch & OPDMASK) == ch)
		EMIT(OCHAR, ch);
	else {
		/*
		 * Kludge: character is too big to fit into an OCHAR operand.
		 * Emit a singleton set.
		 */
		if ((cs = allocset(p)) == NULL)
			return;
		CHadd(p, cs, ch);
		EMIT(OANYOF, (int)(cs - p->g->sets));
	}
}

/*
 - nonnewline - emit REG_NEWLINE version of OANY
 == static void nonnewline(struct parse *p);
 *
 * Boy, is this implementation ever a kludge...
 */
static void
nonnewline(struct parse *p)
{
	char *oldnext = p->next;
	char *oldend = p->end;
	char bracket[4];

	p->next = bracket;
	p->end = bracket+3;
	bracket[0] = '^';
	bracket[1] = '\n';
	bracket[2] = ']';
	bracket[3] = '\0';
	p_bracket(p);
	assert(p->next == bracket+3);
	p->next = oldnext;
	p->end = oldend;
}

/*
 - repeat - generate code for a bounded repetition, recursively if needed
 == static void repeat(struct parse *p, sopno start, int from, int to);
 */
static void
repeat(struct parse *p,
	sopno start,		/* operand from here to end of strip */
	int from,		/* repeated from this number */
	int to)			/* to this number of times (maybe INFINITY) */
{
	sopno finish = HERE();
#	define	N	2
#	define	INF	3
#	define	REP(f, t)	((f)*8 + (t))
#	define	MAP(n)	(((n) <= 1) ? (n) : ((n) == INFINITY) ? INF : N)
	sopno copy;

	if (p->error != 0)	/* head off possible runaway recursion */
		return;

	assert(from <= to);

	switch (REP(MAP(from), MAP(to))) {
	case REP(0, 0):			/* must be user doing this */
		DROP(finish-start);	/* drop the operand */
		break;
	case REP(0, 1):			/* as x{1,1}? */
	case REP(0, N):			/* as x{1,n}? */
	case REP(0, INF):		/* as x{1,}? */
		/* KLUDGE: emit y? as (y|) until subtle bug gets fixed */
		INSERT(OCH_, start);		/* offset is wrong... */
		repeat(p, start+1, 1, to);
		ASTERN(OOR1, start);
		AHEAD(start);			/* ... fix it */
		EMIT(OOR2, 0);
		AHEAD(THERE());
		ASTERN(O_CH, THERETHERE());
		break;
	case REP(1, 1):			/* trivial case */
		/* done */
		break;
	case REP(1, N):			/* as x?x{1,n-1} */
		/* KLUDGE: emit y? as (y|) until subtle bug gets fixed */
		INSERT(OCH_, start);
		ASTERN(OOR1, start);
		AHEAD(start);
		EMIT(OOR2, 0);			/* offset very wrong... */
		AHEAD(THERE());			/* ...so fix it */
		ASTERN(O_CH, THERETHERE());
		copy = dupl(p, start+1, finish+1);
		assert(copy == finish+4);
		repeat(p, copy, 1, to-1);
		break;
	case REP(1, INF):		/* as x+ */
		INSERT(OPLUS_, start);
		ASTERN(O_PLUS, start);
		break;
	case REP(N, N):			/* as xx{m-1,n-1} */
		copy = dupl(p, start, finish);
		repeat(p, copy, from-1, to-1);
		break;
	case REP(N, INF):		/* as xx{n-1,INF} */
		copy = dupl(p, start, finish);
		repeat(p, copy, from-1, to);
		break;
	default:			/* "can't happen" */
		SETERROR(REG_ASSERT);	/* just in case */
		break;
	}
}

/*
 - wgetnext - helper function for WGETNEXT() macro. Gets the next wide
 - character from the parse struct, signals a REG_ILLSEQ error if the
 - character can't be converted. Returns the number of bytes consumed.
 */
static wint_t
wgetnext(struct parse *p)
{
	mbstate_t mbs;
	wchar_t wc;
	size_t n;

	memset(&mbs, 0, sizeof(mbs));
	n = mbrtowc(&wc, p->next, p->end - p->next, &mbs);
	if (n == (size_t)-1 || n == (size_t)-2) {
		SETERROR(REG_ILLSEQ);
		return (0);
	}
	if (n == 0)
		n = 1;
	p->next += n;
	return (wc);
}

/*
 - seterr - set an error condition
 == static int seterr(struct parse *p, int e);
 */
static int			/* useless but makes type checking happy */
seterr(struct parse *p, int e)
{
	if (p->error == 0)	/* keep earliest error condition */
		p->error = e;
	p->next = nuls;		/* try to bring things to a halt */
	p->end = nuls;
	return(0);		/* make the return value well-defined */
}

/*
 - allocset - allocate a set of characters for []
 == static cset *allocset(struct parse *p);
 */
static cset *
allocset(struct parse *p)
{
	cset *cs, *ncs;

	ncs = realloc(p->g->sets, (p->g->ncsets + 1) * sizeof(*ncs));
	if (ncs == NULL) {
		SETERROR(REG_ESPACE);
		return (NULL);
	}
	p->g->sets = ncs;
	cs = &p->g->sets[p->g->ncsets++];
	memset(cs, 0, sizeof(*cs));

	return(cs);
}

/*
 - freeset - free a now-unused set
 == static void freeset(struct parse *p, cset *cs);
 */
static void
freeset(struct parse *p, cset *cs)
{
	cset *top = &p->g->sets[p->g->ncsets];

	free(cs->wides);
	free(cs->ranges);
	free(cs->types);
	memset(cs, 0, sizeof(*cs));
	if (cs == top-1)	/* recover only the easy case */
		p->g->ncsets--;
}

/*
 - singleton - Determine whether a set contains only one character,
 - returning it if so, otherwise returning OUT.
 */
static wint_t
singleton(cset *cs)
{
	wint_t i, s, n;

	for (i = n = 0; i < NC; i++)
		if (CHIN(cs, i)) {
			n++;
			s = i;
		}
	if (n == 1)
		return (s);
	if (cs->nwides == 1 && cs->nranges == 0 && cs->ntypes == 0 &&
	    cs->icase == 0)
		return (cs->wides[0]);
	/* Don't bother handling the other cases. */
	return (OUT);
}

/*
 - CHadd - add character to character set.
 */
static void
CHadd(struct parse *p, cset *cs, wint_t ch)
{
	wint_t nch, *newwides;
	assert(ch >= 0);
	if (ch < NC)
		cs->bmp[ch >> 3] |= 1 << (ch & 7);
	else {
		newwides = realloc(cs->wides, (cs->nwides + 1) *
		    sizeof(*cs->wides));
		if (newwides == NULL) {
			SETERROR(REG_ESPACE);
			return;
		}
		cs->wides = newwides;
		cs->wides[cs->nwides++] = ch;
	}
	if (cs->icase) {
		if ((nch = towlower(ch)) < NC)
			cs->bmp[nch >> 3] |= 1 << (nch & 7);
		if ((nch = towupper(ch)) < NC)
			cs->bmp[nch >> 3] |= 1 << (nch & 7);
	}
}

/*
 - CHaddrange - add all characters in the range [min,max] to a character set.
 */
static void
CHaddrange(struct parse *p, cset *cs, wint_t min, wint_t max)
{
	crange *newranges;

	for (; min < NC && min <= max; min++)
		CHadd(p, cs, min);
	if (min >= max)
		return;
	newranges = realloc(cs->ranges, (cs->nranges + 1) *
	    sizeof(*cs->ranges));
	if (newranges == NULL) {
		SETERROR(REG_ESPACE);
		return;
	}
	cs->ranges = newranges;
	cs->ranges[cs->nranges].min = min;
	cs->ranges[cs->nranges].min = max;
	cs->nranges++;
}

/*
 - CHaddtype - add all characters of a certain type to a character set.
 */
static void
CHaddtype(struct parse *p, cset *cs, wctype_t wct)
{
	wint_t i;
	wctype_t *newtypes;

	for (i = 0; i < NC; i++)
		if (iswctype(i, wct))
			CHadd(p, cs, i);
	newtypes = realloc(cs->types, (cs->ntypes + 1) *
	    sizeof(*cs->types));
	if (newtypes == NULL) {
		SETERROR(REG_ESPACE);
		return;
	}
	cs->types = newtypes;
	cs->types[cs->ntypes++] = wct;
}

/*
 - dupl - emit a duplicate of a bunch of sops
 == static sopno dupl(struct parse *p, sopno start, sopno finish);
 */
static sopno			/* start of duplicate */
dupl(struct parse *p,
	sopno start,		/* from here */
	sopno finish)		/* to this less one */
{
	sopno ret = HERE();
	sopno len = finish - start;

	assert(finish >= start);
	if (len == 0)
		return(ret);
	enlarge(p, p->ssize + len);	/* this many unexpected additions */
	assert(p->ssize >= p->slen + len);
	(void) memcpy((char *)(p->strip + p->slen),
		(char *)(p->strip + start), (size_t)len*sizeof(sop));
	p->slen += len;
	return(ret);
}

/*
 - doemit - emit a strip operator
 == static void doemit(struct parse *p, sop op, size_t opnd);
 *
 * It might seem better to implement this as a macro with a function as
 * hard-case backup, but it's just too big and messy unless there are
 * some changes to the data structures.  Maybe later.
 */
static void
doemit(struct parse *p, sop op, size_t opnd)
{
	/* avoid making error situations worse */
	if (p->error != 0)
		return;

	/* deal with oversize operands ("can't happen", more or less) */
	assert(opnd < 1<<OPSHIFT);

	/* deal with undersized strip */
	if (p->slen >= p->ssize)
		enlarge(p, (p->ssize+1) / 2 * 3);	/* +50% */
	assert(p->slen < p->ssize);

	/* finally, it's all reduced to the easy case */
	p->strip[p->slen++] = SOP(op, opnd);
}

/*
 - doinsert - insert a sop into the strip
 == static void doinsert(struct parse *p, sop op, size_t opnd, sopno pos);
 */
static void
doinsert(struct parse *p, sop op, size_t opnd, sopno pos)
{
	sopno sn;
	sop s;
	int i;

	/* avoid making error situations worse */
	if (p->error != 0)
		return;

	sn = HERE();
	EMIT(op, opnd);		/* do checks, ensure space */
	assert(HERE() == sn+1);
	s = p->strip[sn];

	/* adjust paren pointers */
	assert(pos > 0);
	for (i = 1; i < NPAREN; i++) {
		if (p->pbegin[i] >= pos) {
			p->pbegin[i]++;
		}
		if (p->pend[i] >= pos) {
			p->pend[i]++;
		}
	}

	memmove((char *)&p->strip[pos+1], (char *)&p->strip[pos],
						(HERE()-pos-1)*sizeof(sop));
	p->strip[pos] = s;
}

/*
 - dofwd - complete a forward reference
 == static void dofwd(struct parse *p, sopno pos, sop value);
 */
static void
dofwd(struct parse *p, sopno pos, sop value)
{
	/* avoid making error situations worse */
	if (p->error != 0)
		return;

	assert(value < 1<<OPSHIFT);
	p->strip[pos] = OP(p->strip[pos]) | value;
}

/*
 - enlarge - enlarge the strip
 == static void enlarge(struct parse *p, sopno size);
 */
static void
enlarge(struct parse *p, sopno size)
{
	sop *sp;

	if (p->ssize >= size)
		return;

	sp = (sop *)realloc(p->strip, size*sizeof(sop));
	if (sp == NULL) {
		SETERROR(REG_ESPACE);
		return;
	}
	p->strip = sp;
	p->ssize = size;
}

/*
 - stripsnug - compact the strip
 == static void stripsnug(struct parse *p, struct re_guts *g);
 */
static void
stripsnug(struct parse *p, struct re_guts *g)
{
	g->nstates = p->slen;
	g->strip = (sop *)realloc((char *)p->strip, p->slen * sizeof(sop));
	if (g->strip == NULL) {
		SETERROR(REG_ESPACE);
		g->strip = p->strip;
	}
}

/*
 - findmust - fill in must and mlen with longest mandatory literal string
 == static void findmust(struct parse *p, struct re_guts *g);
 *
 * This algorithm could do fancy things like analyzing the operands of |
 * for common subsequences.  Someday.  This code is simple and finds most
 * of the interesting cases.
 *
 * Note that must and mlen got initialized during setup.
 */
static void
findmust(struct parse *p, struct re_guts *g)
{
	sop *scan;
	sop *start;
	sop *newstart;
	sopno newlen;
	sop s;
	char *cp;
	int offset;
	char buf[MB_LEN_MAX];
	size_t clen;
	mbstate_t mbs;

	/* avoid making error situations worse */
	if (p->error != 0)
		return;

	/*
	 * It's not generally safe to do a ``char'' substring search on
	 * multibyte character strings, but it's safe for at least
	 * UTF-8 (see RFC 3629).
	 */
	if (MB_CUR_MAX > 1 &&
	    strcmp(_CurrentRuneLocale->__encoding, "UTF-8") != 0)
		return;

	/* find the longest OCHAR sequence in strip */
	newlen = 0;
	offset = 0;
	g->moffset = 0;
	scan = g->strip + 1;
	do {
		s = *scan++;
		switch (OP(s)) {
		case OCHAR:		/* sequence member */
			if (newlen == 0) {		/* new sequence */
				memset(&mbs, 0, sizeof(mbs));
				newstart = scan - 1;
			}
			clen = wcrtomb(buf, OPND(s), &mbs);
			if (clen == (size_t)-1)
				goto toohard;
			newlen += clen;
			break;
		case OPLUS_:		/* things that don't break one */
		case OLPAREN:
		case ORPAREN:
			break;
		case OQUEST_:		/* things that must be skipped */
		case OCH_:
			offset = altoffset(scan, offset);
			scan--;
			do {
				scan += OPND(s);
				s = *scan;
				/* assert() interferes w debug printouts */
				if (OP(s) != O_QUEST && OP(s) != O_CH &&
							OP(s) != OOR2) {
					g->iflags |= BAD;
					return;
				}
			} while (OP(s) != O_QUEST && OP(s) != O_CH);
			/* FALLTHROUGH */
		case OBOW:		/* things that break a sequence */
		case OEOW:
		case OBOL:
		case OEOL:
		case O_QUEST:
		case O_CH:
		case OEND:
			if (newlen > g->mlen) {		/* ends one */
				start = newstart;
				g->mlen = newlen;
				if (offset > -1) {
					g->moffset += offset;
					offset = newlen;
				} else
					g->moffset = offset;
			} else {
				if (offset > -1)
					offset += newlen;
			}
			newlen = 0;
			break;
		case OANY:
			if (newlen > g->mlen) {		/* ends one */
				start = newstart;
				g->mlen = newlen;
				if (offset > -1) {
					g->moffset += offset;
					offset = newlen;
				} else
					g->moffset = offset;
			} else {
				if (offset > -1)
					offset += newlen;
			}
			if (offset > -1)
				offset++;
			newlen = 0;
			break;
		case OANYOF:		/* may or may not invalidate offset */
			/* First, everything as OANY */
			if (newlen > g->mlen) {		/* ends one */
				start = newstart;
				g->mlen = newlen;
				if (offset > -1) {
					g->moffset += offset;
					offset = newlen;
				} else
					g->moffset = offset;
			} else {
				if (offset > -1)
					offset += newlen;
			}
			if (offset > -1)
				offset++;
			newlen = 0;
			break;
		toohard:
		default:
			/* Anything here makes it impossible or too hard
			 * to calculate the offset -- so we give up;
			 * save the last known good offset, in case the
			 * must sequence doesn't occur later.
			 */
			if (newlen > g->mlen) {		/* ends one */
				start = newstart;
				g->mlen = newlen;
				if (offset > -1)
					g->moffset += offset;
				else
					g->moffset = offset;
			}
			offset = -1;
			newlen = 0;
			break;
		}
	} while (OP(s) != OEND);

	if (g->mlen == 0) {		/* there isn't one */
		g->moffset = -1;
		return;
	}

	/* turn it into a character string */
	g->must = malloc((size_t)g->mlen + 1);
	if (g->must == NULL) {		/* argh; just forget it */
		g->mlen = 0;
		g->moffset = -1;
		return;
	}
	cp = g->must;
	scan = start;
	memset(&mbs, 0, sizeof(mbs));
	while (cp < g->must + g->mlen) {
		while (OP(s = *scan++) != OCHAR)
			continue;
		clen = wcrtomb(cp, OPND(s), &mbs);
		assert(clen != (size_t)-1);
		cp += clen;
	}
	assert(cp == g->must + g->mlen);
	*cp++ = '\0';		/* just on general principles */
}

/*
 - altoffset - choose biggest offset among multiple choices
 == static int altoffset(sop *scan, int offset);
 *
 * Compute, recursively if necessary, the largest offset among multiple
 * re paths.
 */
static int
altoffset(sop *scan, int offset)
{
	int largest;
	int try;
	sop s;

	/* If we gave up already on offsets, return */
	if (offset == -1)
		return -1;

	largest = 0;
	try = 0;
	s = *scan++;
	while (OP(s) != O_QUEST && OP(s) != O_CH) {
		switch (OP(s)) {
		case OOR1:
			if (try > largest)
				largest = try;
			try = 0;
			break;
		case OQUEST_:
		case OCH_:
			try = altoffset(scan, try);
			if (try == -1)
				return -1;
			scan--;
			do {
				scan += OPND(s);
				s = *scan;
				if (OP(s) != O_QUEST && OP(s) != O_CH &&
							OP(s) != OOR2)
					return -1;
			} while (OP(s) != O_QUEST && OP(s) != O_CH);
			/* We must skip to the next position, or we'll
			 * leave altoffset() too early.
			 */
			scan++;
			break;
		case OANYOF:
		case OCHAR:
		case OANY:
			try++;
		case OBOW:
		case OEOW:
		case OLPAREN:
		case ORPAREN:
		case OOR2:
			break;
		default:
			try = -1;
			break;
		}
		if (try == -1)
			return -1;
		s = *scan++;
	}

	if (try > largest)
		largest = try;

	return largest+offset;
}

/*
 - computejumps - compute char jumps for BM scan
 == static void computejumps(struct parse *p, struct re_guts *g);
 *
 * This algorithm assumes g->must exists and is has size greater than
 * zero. It's based on the algorithm found on Computer Algorithms by
 * Sara Baase.
 *
 * A char jump is the number of characters one needs to jump based on
 * the value of the character from the text that was mismatched.
 */
static void
computejumps(struct parse *p, struct re_guts *g)
{
	int ch;
	int mindex;

	/* Avoid making errors worse */
	if (p->error != 0)
		return;

	g->charjump = (int*) malloc((NC + 1) * sizeof(int));
	if (g->charjump == NULL)	/* Not a fatal error */
		return;
	/* Adjust for signed chars, if necessary */
	g->charjump = &g->charjump[-(CHAR_MIN)];

	/* If the character does not exist in the pattern, the jump
	 * is equal to the number of characters in the pattern.
	 */
	for (ch = CHAR_MIN; ch < (CHAR_MAX + 1); ch++)
		g->charjump[ch] = g->mlen;

	/* If the character does exist, compute the jump that would
	 * take us to the last character in the pattern equal to it
	 * (notice that we match right to left, so that last character
	 * is the first one that would be matched).
	 */
	for (mindex = 0; mindex < g->mlen; mindex++)
		g->charjump[(int)g->must[mindex]] = g->mlen - mindex - 1;
}

/*
 - computematchjumps - compute match jumps for BM scan
 == static void computematchjumps(struct parse *p, struct re_guts *g);
 *
 * This algorithm assumes g->must exists and is has size greater than
 * zero. It's based on the algorithm found on Computer Algorithms by
 * Sara Baase.
 *
 * A match jump is the number of characters one needs to advance based
 * on the already-matched suffix.
 * Notice that all values here are minus (g->mlen-1), because of the way
 * the search algorithm works.
 */
static void
computematchjumps(struct parse *p, struct re_guts *g)
{
	int mindex;		/* General "must" iterator */
	int suffix;		/* Keeps track of matching suffix */
	int ssuffix;		/* Keeps track of suffixes' suffix */
	int* pmatches;		/* pmatches[k] points to the next i
				 * such that i+1...mlen is a substring
				 * of k+1...k+mlen-i-1
				 */

	/* Avoid making errors worse */
	if (p->error != 0)
		return;

	pmatches = (int*) malloc(g->mlen * sizeof(unsigned int));
	if (pmatches == NULL) {
		g->matchjump = NULL;
		return;
	}

	g->matchjump = (int*) malloc(g->mlen * sizeof(unsigned int));
	if (g->matchjump == NULL)	/* Not a fatal error */
		return;

	/* Set maximum possible jump for each character in the pattern */
	for (mindex = 0; mindex < g->mlen; mindex++)
		g->matchjump[mindex] = 2*g->mlen - mindex - 1;

	/* Compute pmatches[] */
	for (mindex = g->mlen - 1, suffix = g->mlen; mindex >= 0;
	    mindex--, suffix--) {
		pmatches[mindex] = suffix;

		/* If a mismatch is found, interrupting the substring,
		 * compute the matchjump for that position. If no
		 * mismatch is found, then a text substring mismatched
		 * against the suffix will also mismatch against the
		 * substring.
		 */
		while (suffix < g->mlen
		    && g->must[mindex] != g->must[suffix]) {
			g->matchjump[suffix] = MIN(g->matchjump[suffix],
			    g->mlen - mindex - 1);
			suffix = pmatches[suffix];
		}
	}

	/* Compute the matchjump up to the last substring found to jump
	 * to the beginning of the largest must pattern prefix matching
	 * it's own suffix.
	 */
	for (mindex = 0; mindex <= suffix; mindex++)
		g->matchjump[mindex] = MIN(g->matchjump[mindex],
		    g->mlen + suffix - mindex);

        ssuffix = pmatches[suffix];
        while (suffix < g->mlen) {
                while (suffix <= ssuffix && suffix < g->mlen) {
                        g->matchjump[suffix] = MIN(g->matchjump[suffix],
			    g->mlen + ssuffix - suffix);
                        suffix++;
                }
		if (suffix < g->mlen)
                	ssuffix = pmatches[ssuffix];
        }

	free(pmatches);
}

/*
 - pluscount - count + nesting
 == static sopno pluscount(struct parse *p, struct re_guts *g);
 */
static sopno			/* nesting depth */
pluscount(struct parse *p, struct re_guts *g)
{
	sop *scan;
	sop s;
	sopno plusnest = 0;
	sopno maxnest = 0;

	if (p->error != 0)
		return(0);	/* there may not be an OEND */

	scan = g->strip + 1;
	do {
		s = *scan++;
		switch (OP(s)) {
		case OPLUS_:
			plusnest++;
			break;
		case O_PLUS:
			if (plusnest > maxnest)
				maxnest = plusnest;
			plusnest--;
			break;
		}
	} while (OP(s) != OEND);
	if (plusnest != 0)
		g->iflags |= BAD;
	return(maxnest);
}